1. Field of the Invention
This invention relates to piezo-electrically actuated hydraulic or pneumatic valves.
2. Discussion of the Prior Art
Piezo-electric actuators for hydraulic and pneumatic valves are known. In prior designs, a stack of piezo-electric actuators was put together in order to obtain sufficient displacement at acceptable voltage levels. In another prior art design, a piezoelectric strip was cantilevered at one end and caused to bend so that the displacement at the other end would be sufficient to actuate a fluid control valve.
In other configurations, disclosed in U.S. patent application Ser. No. 08/392,016 entitled "Piezo Composite Sheet Actuated Valve" and in U.S. patent application Ser. No. 08/391,972 entitled "Piezo-Electrically Actuated Valve," filed on the same day as this application and commonly assigned to Applied Power, Inc., piezo-electrically actuated valves are disclosed in which the piezo-electric actuator is in sheet form and constrained by the housing at opposite edges, with the valve orifice or seat adjacent to the center of the actuator. When the actuator is electrically excited, it bows or cups so as to displace the center portion and vary the flow area between the actuator and the seat.
A problem with using a piezo-electric element as a hydraulic or pneumatic valve actuator is that typically the displacement obtainable is quite limited. Forces obtainable are also quite limited.